Fix sass @import deprecation warnings

[fyliu]

• Fixes Dev: Fix sass @import deprecation warnings by changing to @use #2359

What changes did you make?

• migrated sass @import rules to @use
  • I actually used the sass-migrator package to help with the migration.

    npm install sass-migrator --legacy-peer-deps
    npx sass-migrator module --migrate-deps src/styles/App.scss
    

    After fixing a few initial problems, the tool did the rest.

Why did you make the changes (we will use this info to test)?

• The @import rule is deprecated and will be removed in a future release

Testing

• I'm not sure how to get the warnings to display yet
• But otherwise, the imported variables like background color should still work after this change.

[fyliu]

@fyliu replicate the conditions again and see if this fix is something that'll allow us to upgrade to a higher version of sass. This fix could be useful if it does.

[fyliu]

I'd like to save this until after I'm finished dockerizing the project.